[PATCH 2/2] drm: test: Fix 32-bit issue in drm_buddy_test

[Christian König]

Am 29.03.23 um 13:28 schrieb Jani Nikula:
> On Wed, 29 Mar 2023, Maíra Canal <mcanal at igalia.com> wrote:
>> On 3/29/23 03:55, David Gow wrote:
>>> The drm_buddy_test KUnit tests verify that returned blocks have sizes
>>> which are powers of two using is_power_of_2(). However, is_power_of_2()
>>> operations on a 'long', but the block size is a u64. So on systems where
>>> long is 32-bit, this can sometimes fail even on correctly sized blocks.
>>>
>>> This only reproduces randomly, as the parameters passed to the buddy
>>> allocator in this test are random. The seed 0xb2e06022 reproduced it
>>> fine here.
>>>
>>> For now, just hardcode an is_power_of_2() implementation using
>>> x & (x - 1).
>>>
>>> Signed-off-by: David Gow <davidgow at google.com>
>> As we still didn't consolidate an implementation of is_power_of_2_u64(),
> I just cooked up some patches to try to make is_power_of_2() more
> flexible. I only sent them to the "CI trybot" for a quick spin first,
> will post to lkml later. [1]

In the meantime I'm pushing this to drm-misc-fixes unless somebody has 
some last second objections.

Christian.

>
> BR,
> Jani.
>
>
> [1] https://patchwork.freedesktop.org/series/115785/
>
>> Reviewed-by: Maíra Canal <mcanal at igalia.com>
>>
>> Best Regards,
>> - Maíra Canal
>>
>>> ---
>>>
>>> There are actually a couple of is_power_of_2_u64() implementations
>>> already around in:
>>> - drivers/gpu/drm/i915/i915_utils.h
>>> - fs/btrfs/misc.h (called is_power_of_two_u64)
>>>
>>> So the ideal thing would be to consolidate these in one place.
>>>
>>>
>>> ---
>>>    drivers/gpu/drm/tests/drm_buddy_test.c | 3 ++-
>>>    1 file changed, 2 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/gpu/drm/tests/drm_buddy_test.c b/drivers/gpu/drm/tests/drm_buddy_test.c
>>> index f8ee714df396..09ee6f6af896 100644
>>> --- a/drivers/gpu/drm/tests/drm_buddy_test.c
>>> +++ b/drivers/gpu/drm/tests/drm_buddy_test.c
>>> @@ -89,7 +89,8 @@ static int check_block(struct kunit *test, struct drm_buddy *mm,
>>>    		err = -EINVAL;
>>>    	}
>>>    
>>> -	if (!is_power_of_2(block_size)) {
>>> +	/* We can't use is_power_of_2() for a u64 on 32-bit systems. */
>>> +	if (block_size & (block_size - 1)) {
>>>    		kunit_err(test, "block size not power of two\n");
>>>    		err = -EINVAL;
>>>    	}